Job 40:15-24 KJV

Behold now behemoth, which I made with thee; he eateth grass as an ox. [16] Lo now, his strength is in his loins, and his force is in the navel of his belly. [17] He moveth his tail like a cedar: the sinews of his stones are wrapped together. [18] His bones are as strong pieces of brass; his bones are like bars of iron. [19] He is the chief of the ways of God: he that made him can make his sword to approach unto him. [20] Surely the mountains bring him forth food, where all the beasts of the field play. [21] He lieth under the shady trees, in the covert of the reed, and fens. [22] The shady trees cover him with their shadow; the willows of the brook compass him about. [23] Behold, he drinketh up a river, and hasteth not: he trusteth that he can draw up Jordan into his mouth. [24] He taketh it with his eyes: his nose pierceth through snares.

MacArthur’s notes:

Job 40 MBC - 40:15-24 behemoth. While this is a generic term used commonly in the OT for large cattle or land animals, the description in this passage suggests an extraordinary creature. The hippopotamus has been suggested by the details in the passage (vv. 19-24). However, the short tail of a hippo is hardly consistent with verse 17, where tail could be translated “trunk.” It might refer to an elephant, who could easily be considered “first” or chief of God’s creatures whom only He can control (v. 19).Some believe God is describing His most impressive creation among land animals, the dinosaur species, which fit all the characteristics.

40:23 God was not saying this creature lived in the Jordan River but rather, recognizing that the Jordan was familiar to Job, used it to illustrate how much water this beast could ingest. He could swallow the Jordan! It was a word used to refer to something of enormous size and threatening power.